It is well known the use of the system composed of one or more pistons and connecting rods and a crankshaft to convert the rotary motion of the crankshaft into the reciprocating motion of the pistons, which move inside cylinders forming variable volume chambers, allowing either to harness the energy of an expanding gas like in an internal combustion engine or to transmit energy to a working fluid like in an air compressor.
There are also a number of patents dealing with the subject of arranging the pistons in a circular fashion, mounted on one or two rotors, and forcing their oscillation about the axis of the system. The mechanism to produce such oscillation is generally composed of circular gears, cranks, link connections and sliding pins. U.S. Pat. No. 4,599,976 (Paul V. Meuret) for example, discloses an engine with two pistons mounted to rotate reciprocatingly about a shaft. The reciprocation of the pistons is achieved by means of a crank pin fixed to the shaft of the rotor and a connecting rod swivelably mounted to said crank pin and having a crank fixed to the rotational output shaft.
On the other hand, elliptical gears, which are a special type of non-circular gears, are used in some patents concerning a type of rotary machines which are commonly known as pursuing-piston or cat-and-mouse machines. In these machines, two rotors, each one carrying a number of pistons, fully rotate inside a housing while angularly reciprocating relative to one another. The relative angular reciprocation in this type of engines is sometimes achieved through the use of a gear train with elliptical gears. In U.S. Pat. No. 1,482,628 (Frank A. Bullington), a train composed of two circular gears and two elliptical gears are mounted on two shafts which rotate about stationary axes. In U.S. Pat. No. 3,430,573 (Eugen Groeger) the same arrangement is used except for the use of four elliptical gears or, alternatively, two elliptical gears and two circular gears mounted eccentrically. U.S. Pat. No. 3,769,946 (William A. Scherrer) describes several such gear trains to achieve the same objective. The closest prior art document may be considered U.S. Pat. No. 1,701,534 (Rudolph Knopp), which discloses another pursuing-piston type rotary engine characterized in that each of the two rotors is driven by a four-lobe non-circular ring gear and wherein these two ring gears are linked by means of a common elliptical sun gear in mesh with four planetary gears, two of them meshing in turn with one rotor and the other two with the other rotor. Thus, the main differences from the invention as claimed are: two fully rotating rotors as opposed to one oscillating rotor, the presence of a sun gear, the lack of any planet carrier and the absence of any coaxial planet gears.